Fundamental Understanding Research Articles

Tying a true topological protein knot by cyclization

Knotted proteins are fascinating to biophysicists because of their robust ability to fold into intricately defined three-dimensional structures with complex and topologically knotted arrangements. Exploring the biophysical properties of the knotted proteins is of significant interest, as they could offer enhanced chemical, thermal, and mechanostabilities. A true mathematical knot requires a closed path; in contrast, knotted protein structures have open N- and C-termini. To address the question of how a truly knotted protein differs from the naturally occurring counterpart, we enzymatically cyclized a 31 knotted YibK protein from Haemophilus influenza (HiYibK) to investigate the impact of path closure on its structure-function relationship and folding stability. Through the use of a multitude of structural and biophysical tools, including X-ray crystallography, NMR spectroscopy, small angle X-ray scattering, differential scanning calorimetry, and isothermal calorimetry, we showed that the path closure minimally perturbs the native structure and ligand binding of HiYibK. Nevertheless, the cyclization did alter the folding stability and mechanism according to chemical and thermal unfolding analysis. These molecular insights contribute to our fundamental understanding of protein folding and knotting that could have implications in the protein design with higher stabilities.

Synthesis of Tridecacene by Multistep Single-Molecule Manipulation.

Acenes represent a unique class of polycyclic aromatic hydrocarbons that have fascinated chemists and physicists due to their exceptional potential for use in organic electronics. While recent advances in on-surface synthesis have resulted in higher acenes up to dodecacene, a comprehensive understanding of their fundamental properties necessitates their expansion toward even longer homologues. Here, we demonstrate the on-surface synthesis of tridecacene via atom-manipulation-induced conformational preparation and dissociation of a trietheno-bridged precursor on a Au(111) surface. The generated tridecacene has been investigated by scanning tunneling microscopy and spectroscopy (STM/STS), combined with first-principles calculations. We observe that the STS transport gap (1.09 eV) shrinks again following the gap reopening of dodecacene (1.4 eV). Spin-polarized density functional theory calculations confirm an antiferromagnetic open-shell ground-state electronic configuration for tridecacene in the gas phase. Interestingly, tridecacene's open-shell character is significantly reduced upon interaction with the Au(111) surface despite being only physisorbed. The interaction with the surface leads to a lowering of the magnetization of tridecacene, a reduced gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO), compared to the gas phase, and a reduced relative energy to the nonmagnetic state, making it nearly isoenergetic. These observations show qualitatively that the influence of the Au(111) substrate on the properties of long acenes is significant, which is important for interpreting the measured STS transport gaps. Our work contributes to a fundamental understanding of the electronic properties of long acenes, confirming a nonmonotonous length-dependent HOMO-LUMO gap, and to the development of multistep tip-assisted synthesis of elusive compounds.

Magnetic field enhanced surface reconstruction of Fe2P and the promotional effect in electrochemical oxygen evolution

In recent years, the utilization of magnetic fields to enhance the oxygen evolution reaction (OER) performance of catalysts has emerged as an effective approach. However, current research primarily focusing on the impact on magnetic transition metal oxides, and the relevant mechanisms are still worth further exploration. Here, the OER performance of Fe2P loaded on carbon paper (Fe2P/CP) and nickel foam (Fe2P/NF) substrates under in situ magnetic field was investigated. It is revealed that magnetic fields can substantially enhance the OER performance of Fe2P/CP and Fe2P/NF. With a magnetic field of 1.0 T, the current density of 75-Fe2P/CP increases by 28 times (1.8 V vs. RHE), leading to a maximum magnetic current density percentage of 2770%. According to our results, the magnetic enhancement effect is highly correlated with the surface reconstruction of Fe2P to α-FeOOH with lower OER energy barriers. Additionally, the spin pinning effect is observed on the α-FeOOH/Fe2P interfaces, which leads to the rapid alignment of spin electrons on the surface of catalysts under magnetic field, lowering the OO coupling energy barrier, and therefore improve OER kinetics. These discoveries have the potential to contribute to a fundamental and comprehensive understanding of electrochemical reactions involving magnetic fields.

Bubble deformation and breakup in a non-uniform electric field

In this paper, the deformation and breakup characteristics of bubbles during their growth in a mixture solution were studied with a needle-ring electrode configuration in the presence of an electric field by using high-speed photography. Four distinct bubble breakup behaviors of the dripping, cone, kink and branch regimes were achieved successfully by manipulating the electric field. By considering the applied voltage and gas flow rate, the cone structure, interface stability, departure frequency and bubble size distribution in different regimes were quantitatively discussed. It is found that the cone height, interface curvature, departure frequency and bubble size distribution are evidently associated with bubble breakup regimes. As the electric field strength increased, the bubbles stretched in the direction of the electric field and the instability of the gas–liquid interface became stronger, which eventually resulted in the bubbles fragmenting into a cluster of microbubbles. This work provides a fundamental understanding of bubble deformation and breakup mechanisms under the electric field.

Catalytic aerobic oxidation of lignin-based vanillyl alcohol over LaFeO3 perovskite towards vanillin production: Relationships between the activity and acid-base property as well as oxygen vacancy

Developing high-performance acid-base catalysis over perovskite for alcohol aerobic oxidation has received increasing attention, but the fundamental understanding of its surface acid-base property and performance relationship remains largely unknown. Accordingly, a series of LaFeO3 perovskites were fabricated via modified Pechini approach with the addition of different chelating agents to modulate their respective acid-base amount and oxygen vacancy concentration, which subsequently were employed in the aerobic oxidation of vanillyl alcohol (a lignin model), to generate vanillin for elucidating the relationships between the catalytic activity of LaFeO3 perovskite and its acid-base property as well as oxygen vacancy. The results demonstrated that existence of non-linear relationships between the vanillin yield and the acid-base amount as well as oxygen vacancy concentration of LaFeO3 catalyst. Moreover, neither acid-base sites nor oxygen vacancies were the solely factors affecting the activity of LaFeO3 perovskite towards vanillyl alcohol oxidation for vanillin production. Mechanism studies proclaimed that the reactive oxygen species derived from the adsorption of molecule oxygen on oxygen vacancies generated by anion defects combing with Lewis acid sites (Fe3+/Fe2+) to yield FeOx active pairs, which jointly dominated the pathway for vanillyl alcohol oxidation to produce vanillin. Overall, this work offers guidance for designing effective perovskite-based catalysts for lignin conversion to produce value-added chemicals by selectively modulating its acid-base property and oxygen vacancy.

Investigating the coupling between transport and reaction within a catalyst pellet using operando magnetic resonance spectroscopic imaging

In heterogeneous catalysis, the distribution of reactant and product species within a catalyst pellet are of central importance to the catalyst performance, and ultimately to the overall conversion and selectivity achieved in commercial-scale reactors. Despite this importance, fundamental understanding of pellet scale behaviour at operando conditions is limited due to the coupled, multi-scale nature of the underlying transport processes, and the limited techniques capable of mapping the intra-pellet composition at industrially relevant length scales. Here, we demonstrate the coupling between transport and reaction at the pellet scale by using operando magnetic resonance spectroscopic imaging (MRSI) to map the liquid composition within Pd/γ-Al2O3 catalyst pellets at an isotropic in-plane spatial resolution of 86 µm during a styrene hydrogenation reaction. The results reveal that asymmetric liquid wetting at the pellet surface, typical of that occurring in trickle-bed reactors, causes significant composition heterogeneity across a catalyst pellet. Due to the wetting inhomogeneity, commonly used 1D reaction-diffusion models are inadequate for describing the observed composition heterogeneity across the pellet. The results reported here provide unique experimental insight into the coupling between transport and reaction at the pellet scale within an operating reactor.

Computational investigation of the interaction mechanisms of low‐density polyethylene (LDPE)/polyurethane and low‐density polyethylene (LDPE)/hexane systems as absorbents for oil spill remediation: A DFT study

AbstractThe escalating frequency of oil spill incidents and industrial wastewater discharges necessitates the development of effective remediation strategies. In this study, we conduct a comprehensive computational investigation using density functional theory (DFT) to elucidate the interaction mechanisms within polyethylene (PE) combined with polyurethane (PU) and hexane. The study focuses on adsorption energies, intermolecular interactions, miscibility, and electronic properties, providing a molecular‐level understanding crucial for designing advanced absorbent materials. The investigation reveals that the low‐density polyethylene/polyurethane (LDPE/PU) system exhibits significantly higher adsorption energies (−12.87 kcal/mol) compared to PE/hexane (−7.66 kcal/mol), indicating a robust binding affinity. This discrepancy underscores the superior performance of PE/PU as an absorbent material. The enthalpy results, with ∆H values of −55.75 kcal/mol for PE/hexane‐n‐hexadecane and −66.11 kcal/mol for PE/PU‐n‐hexadecane complexes at 298.15 K, support exothermic adsorption. The more exothermic ∆H for PE/PU indicates stronger interactions during oil absorption than PE/hexane. Additionally, Gibbs free energy change (∆G) values affirm a more favorable process for PE/PU, exhibiting a lower ∆G (−42.54 kcal/mol) compared to PE/hexane (−34.79 kcal/mol). Non‐covalent interaction (NCI) studies confirm the importance of van der Waals forces in both systems, validating their role in the adsorption process. Miscibility studies indicate limited interactions, with PE/PU showing positive enthalpy of mixing. Electronic study demonstrates PE/PU's higher energy gap of 9.19 eV, correlating with superior performance. This research contributes to the fundamental understanding of oil absorption processes and informs the design and optimization of environmentally sustainable and efficient oil‐absorbing materials for remediation applications.Highlights DFT explores polymeric systems, PE/PU and PE/hexane, for oil absorbent. PE/PU excels with −12.87 kcal/mol adsorption energy, surpassing PE/hexane (−7.66 kcal/mol). NCI validates van der Waals forces in both systems, crucial for effective adsorption. Miscibility studies reveal limited interactions. PE/PU's superior 9.19 eV energy gap signifies enhanced absorbent performance. PE/PU excels as an oil‐absorbent material, underlining its overall superiority.

Understanding the influence of sulfur configuration on the electrochemical reaction pathway for lithium storage in molybdenum sulfides

Molybdenum sulfides are highly regarded as conversion-type electrodes with exceptional performance potential in lithium-ion batteries (LIBs). However, elucidating their lithium (Li) storage behavior has proven challenging due to the intricate sulfur (S) coordination with molybdenum atoms, which has impeded the realization of high energy densities in future Li storage systems. In this study, we investigate the electrochemical redox reaction pathways of molybdenum sulfide, specifically exploring the impact of various S configurations, including terminal, bridging, and apical S. We employ a comprehensive approach, involving extensive electrochemical measurements and depth X-ray photoelectron spectroscopy (XPS) profiling. In contrast to the multi-step conversion reactions observed in MoS2, sulfur-enriched molybdenum sulfides exhibit a unique single-step Li-ion storage mechanism. As a consequence of the pronounced effect of S configuration on the activation energy barrier during charging and discharging, the redox reaction voltage with Li ions exhibits variations. This versatility verifies that molybdenum sulfides have the potential to serve as both anode and cathode materials in lithium-ion batteries. Furthermore, we propose the incorporation of reduced graphene oxide (rGO) composites to address inherent limitations of molybdenum sulfides, including low electrical conductivity and irreversible reactions. The robust interaction between molybdenum sulfides and oxygen functional groups in rGO enhances rate capability and ensures a stable cycling lifespan. Through this systematic investigation, we suggest a comprehensive insight into the electrochemical reaction pathways governing Li storage behavior in molybdenum sulfides with distinct S configurations. This contributes to the fundamental understanding of these materials and their potential applications in advanced energy storage systems.

Openfoam Simulations for Development of a Mist Flow Diverter in Aerosol Jet Printing

The Aerosol Jet® (AJ) direct-write technology enables material deposition for producing micron-scale fine features on various substrates with almost arbitrary geometry, which is of particular interest in manufacturing 3D conformal electronics among other applications. It operates by delivering an aerosol mist stream consisting of micron-size “ink” droplets, through an aerodynamic focusing nozzle with co-flowing sheath gas in a tapered channel, to the substrate several millimetres away with an impinging jet flow [1]. The ink pattern produced with AJ printing is essentially controlled in a “vector drawing mode” by the relative motion of the substrate with respect to the deposition nozzle. When a constant mist flow rate is fed into the deposition head, a mechanism for stopping the mist flow toward substrate must be implemented to prevent ink deposition in places where ink is undesired along the substrate moving toolpath. In other words, the mist stream toward substrate needs to be switched off at the time when the places of substrate where ink deposition is unwanted are moved under the AJ deposition nozzle, and to be switched on at the time when ink deposition is wanted. For the mist flow toward substrate, it can be considered as a function of time with on or off at certain time points. Here we describe a vacuum-boost diverter for rapid mist flow on-and-off switching in AJ printing, with OpenFOAM® simulations to aid its development and to offer fundamental understanding of its operational behaviour.

Dissecting the geometric and hydrophobic constraints of stapled peptides.

Stapled peptides are a promising class of molecules with potential as highly specific probes of protein-protein interactions and as therapeutics. Hydrocarbon stapling affects the peptide properties through the interplay of two factors: enhancing the overall hydrophobicity and constraining the conformational flexibility. By constructing a series of virtual peptides, we study the role of each factor in modulating the structural properties of a hydrocarbon-stapled peptide PM2, which has been shown to enter cells, engage its target Mouse Double Minute 2 (MDM2), and activate p53. Hamiltonian replica exchange molecular dynamics (HREMD) simulations suggest that hydrocarbon stapling favors helical populations of PM2 through a combination of the geometric constraints and the enhanced hydrophobicity of the peptide. To further understand the conformational landscape of the stapled peptides along the binding pathway, we performed HREMD simulations by restraining the peptide at different distances from MDM2. When the peptide approaches MDM2, the binding pocket undergoes dehydration which appears to be greater in the presence of the stapled peptide compared with the linear peptide. In the binding pocket, the helicity of the stapled peptide is increased due to the favorable interactions between the peptide residues as well as the staple and the microenvironment of the binding pocket, contributing to enhanced affinity. The dissection of the multifaceted mechanism of hydrocarbon stapling into individual factors not only deepens fundamental understanding of peptide stapling, but also provides guidelines for the design of new stapled peptides.

Liquid Structure and Hydrogen Bonding in Aqueous Hydroxylammonium Nitrate.

Hydroxylammonium nitrate (HAN) has emerged as a promising component in ionic liquid-based spacecraft propellants. However, the physicochemical and structural properties of aqueous HAN have been largely overlooked. The purpose of this study is to investigate the hydrogen bonding in aqueous HAN and understand its implications on these properties and the proton transfer mechanism as a function of concentration. Classical polarizable molecular dynamics simulations have been employed with the APPLE&P force field to analyze the geometry of individual hydrogen bonds and the overall hydrogen-bonding network in various concentrations of aqueous HAN. Radial distribution functions (RDFs) and spatial distribution functions (SDFs) indicate the structural arrangement of the species and their hydrogen bonds. Projections of water density and the orientation of its electric dipole moment near the ions provide insight into the hydrogen-bonding network. The incorporation of water into the hydrogen-bonding network at high ion concentrations occurs via interstitial accommodation around the ions immediately outside the first solvation shell. While ion pairs are observed at all concentrations considered, the frequency of Ha···On hydrogen bonds increases substantially with the ion concentration. The findings contribute to a better fundamental understanding of HAN and the precursors of reactivity, crucial to the development of "green" spacecraft propellants.

Active hydraulics laws from frustration principles

Viscous flows are laminar and deterministic. Robust linear laws accurately predict their streamlines in geometries as complex as blood vessels, porous media and pipe networks. However, biological and synthetic active fluids defy these fundamental laws. Irrespective of their microscopic origin, confined active flows are intrinsically bistable, making it challenging to predict flows in active fluid networks. Although early theories attempted to tackle this problem, quantitative experiments to validate their relevance to active hydraulics are lacking. Here we present a series of laws that accurately predict the geometry of active flows in trivalent networks. Experiments with colloidal rollers reveal that active hydraulic flows realize dynamical spin ices: they are frustrated, non-deterministic and yield degenerate streamline patterns. These patterns split into two geometric classes of self-similar loops, which reflect the fractionalization of topological defects at subchannel scales. Informed by our measurements, we formulate the laws of active hydraulics in trivalent networks as a double-spin model. We then use these laws to predict the random geometry of degenerate streamlines. We expect our fundamental understanding to provide robust design rules for active microfluidic devices and to offer avenues to investigate the motion of living cells and organisms in complex habitats.

Abstract IA024: Mechanistic insights into how RADX regulates RAD51 nucleoprotein filaments to maintain genome stability and control replication stress responses

Abstract RAD51 nucleoprotein filaments are central to maintaining genome stability, governing crucial processes like homology-directed double-strand break repair, replication fork reversal, and shielding replication forks from nucleases. The precise regulation of RAD51 filament formation and stability is critical for these functions, which suppress tumorigenesis and determine cellular responses to common cancer therapies. RADX is a pivotal regulator of RAD51 in the context of DNA replication, impacting replication fork reversal and fork stabilization. After identifying RADX as an RPA-related RAD51 regulator, we have worked to understand how it acts, thereby elucidating its role in genome stability and its influence on cancer cell responses to PARP inhibitors and chemotherapies. Genetically, RADX exhibits a dual role, capable of either inhibiting or promoting replication fork reversal based on the levels of replication stress. Biochemical studies show that RADX has inhibitory effects on RAD51 strand exchange and D-loop formation activities, achieved through direct binding to single-strand DNA and RAD51, along with the stimulation of RAD51 ATP hydrolysis. These activities collectively destabilize RAD51 nucleofilaments, opposing the stabilizing effects of BRCA2. Cells lacking RADX regulatory functions exhibit replication defects, DNA damage accumulation, reduced growth, and heightened sensitivity to DNA damage and replication stress. Structural analyses, including cryo-electron microscopy and mass photometry, revealed how RADX binds ssDNA and show it exists in multiple oligomeric states with a preference for trimers when bound to single-stranded DNA. Negative stain electron microscopy imaging supports a model wherein RADX functions by capping and restricting the growing ends of RAD51 filaments. In summary, our findings provide a comprehensive understanding of the regulatory mechanisms governing RAD51 nucleofilament dynamics by RADX, emphasizing its crucial role in coordinating replication fork stability and genome integrity. This knowledge not only contributes to the fundamental understanding of cellular processes but also offers insights into potential therapeutic interventions targeting RAD51-controlled pathways. Citation Format: Madison Adolph, Swati Balakrishnan, Walter Chazin, David Cortez. Mechanistic insights into how RADX regulates RAD51 nucleoprotein filaments to maintain genome stability and control replication stress responses [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: DNA Damage Repair: From Basic Science to Future Clinical Application; 2024 Jan 9-11; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2024;84(1 Suppl):Abstract nr IA024.

Messenger RNA Therapy for Female Reproductive Health.

Female reproductive health has traditionally been an underrepresented area of research in the drug delivery sciences. This disparity is also seen in the emerging field of mRNA therapeutics, a class of medicines that promises to treat and prevent disease by upregulating protein expression in the body. Here, we review advances in mRNA therapies through the lens of improving female reproductive health. Specifically, we begin our review by discussing the fundamental structure and biochemical modifications associated with mRNA-based drugs. Then, we discuss various packaging technologies, including lipid nanoparticles, that can be utilized to protect and transport mRNA drugs to target cells in the body. Last, we conclude our review by discussing the usage of mRNA therapy for addressing pregnancy-related health and vaccination against sexually transmitted diseases in women. Of note, we also highlight relevant clinical trials using mRNA for female reproductive health while also providing their corresponding National Clinical Trial identifiers. In undertaking this review, our aim is to provide a fundamental background understanding of mRNA therapy and its usage to specifically address female health issues with an overarching goal of providing information toward addressing gender disparity in certain aspects of health research.

Elevated temperature effects (T > 100 °C) on the interfacial water and microstructure swelling of Na-montmorillonite

Montmorillonite-based barriers are key elements of the engineered barrier systems (EBS) in geological disposal facilities (GDF). Their performance at temperatures above 100 °C is not sufficiently understood to assess the possibility of raising the temperature limits in GDF designs that could reduce construction costs and CO2 footprint. The present work provides new fundamental insights through molecular dynamics (MD) simulations of Na-montmorillonite's water-clay interactions and swelling pressure at temperatures 298–500 K and basal spacings of 1.5–3.5 nm. At temperatures above 100 °C, the swelling behaviour is governed by the attractive van der Waals force and the repulsive hydration force instead of the repulsive electrostatic (double layer) force. The swelling pressure reduction with increasing temperature is related to the weakened hydration repulsion and electric double layer repulsion, which result from the deterioration of the interlayer water layer structure and the shrinkage of the electric double layer. The applicability and breakdown of the classic Derjaguin-Landau-Verwey-Overbeek (DLVO) theory at elevated temperatures are examined. By excluding the osmotic contribution in the DLVO theory, the summation of the van der Waals interaction in DLVO and an additional non-DLVO hydration interaction can predict our MD system's swelling under high temperatures. The findings of this study provide a fundamental understanding of the swelling behaviour and the underlying molecular-level mechanisms of the clay microstructure under extreme conditions.

Techniques, Advantages and Limitations of Neuroimaging: A Systematic Review

Neuroimaging was developed as a non-invasive and objective technique for studying the function and structure of the normal human brain, utilizing quantitative computational methods. The utilization of quantitative research in the study of neurological and mental health disorders is experiencing a notable increase. While there are post-residency programs offered in the field of Neuro-Radiology, it is important to note that neuroimaging is not recognized as an independent medical specialty. An increasing number of studies are placing emphasis on matters pertaining to rehabilitation. Hence, possessing a fundamental understanding of the prevailing neuroimaging approaches is crucial for comprehending and analyzing this rapidly evolving research area. This article provides an overview of the signal source, reviews the advantages and limitations associated with the techniques, and presents a comprehensive evaluation of the field. Functional magnetic resonance imaging (fMRI) has materialized as a prominent tool within the realm of rehabilitation science due to its widespread utilization and significance.

Impact of Surface Chemistry on Emulsion-Electrode Interactions and Electron-Transfer Kinetics in the Single-Entity Electrochemistry.

Single-entity electrochemistry (SEE) provides powerful means to track a single particle, single cell, and even single molecule from the nano to microscale. The electrode serves as not only the detector of collision but also the surface supplier in SEE, and the fundamental understanding of the electrode surface chemistry on the dynamic particle-electrode interactions and electrochemical responses of a single particle still remains unexplored, particularly for soft particles. Herein, dynamic interactions of microemulsions and the interaction-controlled electron-transfer (ET) kinetics are studied employing SEE and fluorescence spectroscopy. The o/w-type nitrobenzene emulsions were prepared with the surfactant-type room temperature ionic liquids (RTILs). Biased the electrode potential for the reduction of 7,7,8,8-tetracyanoquinodimethane within emulsions, it is surprising to see the distinct collision current signals on the carbon fiber ultramicroelectrode (C UME) and Au ultramicroelectrode (Au UME) in the late stage of chronoamperometric measurements. Theoretical understanding was made to determine the ET kinetics behind the disparate current signals. It is believed that the electrode surface chemistry, i.e., the surface energy, has a great influence on the dynamic emulsion-electrode interactions and ET kinetics. On the hydrophilic surface of Au UME, emulsions tend to decompose/detach from the electrode surface immediately after colliding. In contrast, on the lipophilic surface of C UME with lower surface energy, a layer of oil phase accumulated by the coalescence of emulsions and the migration of the precedent colliding emulsions, which would serve as a barrier to block ET via tunneling as manifested by the gradual slowdown of ET rate and the reduced collision frequency in the late stage of measurement. The impacts of the emulsion size and amphiphilicity of RTILs on the C UME-emulsion interactions and ET kinetics were also investigated.

Synergistic effect of Mn and B on the cohesive properties of grain boundaries in Ni3Al: A first-principles study

Ni-based superalloys are known as potential structural materials under extreme conditions due to their good high temperature properties. However, some alloys such as Ni3Al exhibit intrinsic brittleness which severely restricts their practical applications as structural materials. It is well known that the moderate addition of B can significantly improve the ductility of Ni3Al grain boundaries (GB) but restricted to the Ni-rich side. Adding Mn together with B can improve the ductility of Ni3Al in a wider composition range. To provide some fundamental understandings on such a cooperative effect, the segregation of Mn or/and B to the Ni3Al GBs and their effects on the cohesive properties of the GBs are systematically investigated by using a first-principles method. It is shown that B tends to segregate to the Ni-rich holes of the GBs, which means that B prefers to form stronger covalent bonds with the Ni atoms. The calculation of Griffith’s work shows its improved effect on the cohesion of the GBs. Different from site occupation tendency in bulk Ni3Al, Mn tends to segregate to the GBs and substitute the Ni sites at the GBs. It is interesting to notice that B can segregate to the Ni-deficient hole and improve the cohesive properties of the GBs in the presence of Mn substituting Ni atoms at the GBs. Whether at the Ni-rich holes or Ni-deficient holes of B segregation, Mn substituting the Al sites won’t take place at the GBs. The improvement of the ductility of composition-dependent Ni3Al extends from the Ni-rich side to the stoichiometric side with the co-doping of Mn and B. The electronic structure mechanism behind is discussed based on the calculated electronic density of states. It is suggested that the beneficial cooperative effect of Mn and B on the cohesive properties of the GBs is attributable to the increasing B-Al interaction.

Creep in a nanocrystalline VNbMoTaW refractory high-entropy alloy

Refractory high-entropy alloys (RHEAs) are considered to be a promising candidate for elevated temperature applications. Nanocrystalline (NC) RHEAs are supposed to exhibit many different high-temperature mechanical behaviors in comparison with their coarse-grained (CG) and ultrafine-grained (UFG) counterparts. However, the creep behaviors of NC RHEAs, which must be well evaluated for high-temperature applications, are largely unknown because it is difficult to produce bulk quantities of NC RHEAs for creep tests. In the present work, an equiatomic bulk NC VNbMoTaW RHEA with an average grain size of 67 ± 17 nm was synthesized by mechanical alloying (MA) and the subsequent high-pressure/high-temperature sintering. The creep tests were performed on bulk specimens by compression at high temperatures (973 and 1073 K) under different stresses (70–1100 MPa). The creep resistance of the bulk NC VNbMoTaW is slightly lower than that of the bulk CG VNbMoTaW, but much higher than that of previously reported CG and UFG HEAs. The derived activation volume, stress exponent, and activation energy of bulk NC VNbMoTaW indicate that the creep deformation is dominated by grain boundary diffusion. The creep deformation is controlled by the diffusion of Mo and Nb elements, which have the two slowest grain boundary diffusivities among the five alloying elements. The present work provides a fundamental understanding of the creep behavior and deformation mechanism of NC RHEAs, which should help design advanced creep-resistant RHEAs.

A Critical Analysis of Chemical and Electrochemical Oxidation Mechanisms in Li-Ion Batteries.

Electrolyte decomposition limits the lifetime of commercial lithium-ion batteries (LIBs) and slows the adoption of next-generation energy storage technologies. A fundamental understanding of electrolyte degradation is critical to rationally design stable and energy-dense LIBs. To date, most explanations for electrolyte decomposition at LIB positive electrodes have relied on ethylene carbonate (EC) being chemically oxidized by evolved singlet oxygen (1O2) or electrochemically oxidized. In this work, we apply density functional theory to assess the feasibility of these mechanisms. We find that electrochemical oxidation is unfavorable at any potential reached during normal LIB operation, and we predict that previously reported reactions between the EC and 1O2 are kinetically limited at room temperature. Our calculations suggest an alternative mechanism in which EC reacts with superoxide (O2-) and/or peroxide (O22-) anions. This work provides a new perspective on LIB electrolyte decomposition and motivates further studies to understand the reactivity at positive electrodes.